Underscore, Underscore.string and RequireJS

main.js

requirejs.config({
  paths: {
    'backbone'            : '../lib/backbone/backbone',
    'backbone.base'       : '../lib/backbone/backbone.base',
    'backbone.extensions' : '../lib/backbone/backbone.extensions',
    'jquery'              : '../lib/jquery/jquery',
    'text'                : '../lib/require/text',
    'underscore'          : '../lib/underscore/underscore',
    'underscore.mixed'    : '../lib/underscore/underscore.mixed',
    'underscore.string'   : '../lib/underscore/underscore.string'
  },
  shim: {
    'backbone.base': {
      deps: ['underscore.mixed', 'jquery'],
      exports: 'Backbone'
    },
  }
});

underscore.mixed.js

define([
  'underscore',
  'underscore.string'
], function(_, _s) {
  _.mixin(_s.exports());
  return _;
});